Circular RNA - New member of noncoding RNA with novel functions

A growing body of evidence indicates that circular RNAs are not simply a side product of splicing but a new class of noncoding RNAs in higher eukaryotes. The progression for the studies of circular RNAs is accelerated by combination of several advanced technologies such as next generation sequencing, gene silencing (small interfering RNAs) and editing (CRISPR/Cas9). More and more studies showed that dysregulated expression of circular RNAs plays critical roles during the development of several human diseases. Herein, we review the current advance of circular RNAs for their biosynthesis, molecular functions, and implications in human diseases. Impact statement The accumulating evidence indicate that circular RNA (circRNA) is a novel class of noncoding RNA with diverse molecular functions. Our review summarizes the current hypotheses for the models of circRNA biosynthesis including the direct interaction between upstream and downstream introns and lariat-driven circularization. In addition, molecular functions such as a decoy of microRNA (miRNA) termed miRNA sponge, transcriptional regulator, and protein-like modulator are also discussed. Finally, we reviewed the potential roles of circRNAs in neural system, cardiovascular system as well as cancers. These should provide insightful information for studying the regulation and functions of circRNA in other model of human diseases.